Deep inelastic electron-photon scattering is studied in the Q**2 range from 1.2 to 30 GeV**2 using the LEP1 data taken with the ALEPH, L3 and OPAL detectors at centre-of-mass energies close to the mass of the Z boson. Distributions of the measured hadronic final state are corrected to the hadron level and compared to the predictions of the HERWIG and PHOJET Monte Carlo models. For large regions in most of the distributions studied the results of the different experiments agree with one another. However, significant differences are found between the data and the models. Therefore the combined LEP data serve as an important input to improve on the Monte Carlo models.
The combined energy flow (DE/DETARAP) separately for the low and high Q**2 regions. The data are corrected using the HERWIG-kt model.
The combined energy flow (DE/DETARAP) separately for the low and high Q**2 regions. The data are corrected using the PHOJET model.
The interaction of virtual photons is investigated using double tagged gammagamma events with hadronic final states recorded by the ALEPH experiment at e^+e^- centre-of-mass energies between 188 and 209 GeV. The measured cross section is compared to Monte Carlo models, and to next-to-leading-order QCD and BFKL calculations.
Differential cross section as a function of the relative energy of the scattered electrons.
Distributions are presented of event shape variables, jet roduction rates and charged particle momenta obtained from 53 000 hadronicZ decays. They are compared to the predictions of the QCD+hadronization models JETSET, ARIADNE and HERWIG, and are used to optimize several model parameters. The JETSET and ARIADNE coherent parton shower (PS) models with running αs and string fragmentation yield the best description of the data. The HERWIG parton shower model with cluster fragmentation fits the data less well. The data are in better agreement with JETSET PS than with JETSETO(αS2) matrix elements (ME) even when the renormalization scale is optimized.
Jet mass difference distribution.
The production rates and the inclusive cross sections of the isovector meson${\rm \pi^0}$, the isoscalar mesons$\eta$and
Inclusive cross section for K0S production in three-jet events where the K0S comes from JET3.
Previously published and as yet unpublished QCD results obtained with the ALEPH detector at LEP1 are presented. The unprecedented statistics allows detailed studies of both perturbative and non-perturbative aspects of strong interactions to be carried out using hadronic Z and tau decays. The studies presented include precise determinations of the strong coupling constant, tests of its flavour independence, tests of the SU(3) gauge structure of QCD, study of coherence effects, and measurements of single-particle inclusive distributions and two-particle correlations for many identified baryons and mesons.
Unfolded values of the the mean multiplicity and dispersion of the multiplicity distributions integrated over the rapidity region -1.5 to 1.5.
Earlier measurements at LEP of isolated hard photons in hadronic Z decays, attributed to radiation from primary quark pairs, have been extended in the ALEPH experiment to include hard photon productioninside hadron jets. Events are selected where all particles combine democratically to form hadron jets, one of which contains a photon with a fractional energyz≥0.7. After statistical subtraction of non-prompt photons, the quark-to-photon fragmentation function,D(z), is extracted directly from the measured 2-jet rate. By taking into account the perturbative contributions toD(z) obtained from anO(ααs) QCD calculation, the unknown non-perturbative component ofD(z) is then determined at highz. Provided due account is taken of hadronization effects nearz=1, a good description of the other event topologies is then found.
2-jet events. Variable Z has been defined as E(gamma)/(E(gamma)+E(had)), where E(gamma) is the energy of the hard photon in 'photon-jet', E(had) is the energy of the rest hadrons in jet. Ycut is jet resolution parameter (see paper).
2-jet events. Variable Z has been defined as E(gamma)/(E(gamma)+E(had)), where E(gamma) is the energy of the hard photon in 'photon-jet', E(had) is the energy of the rest hadrons in jet. Ycut is jet resolution parameter (see paper).
2-jet events. Variable Z has been defined as E(gamma)/(E(gamma)+E(had)), where E(gamma) is the energy of the hard photon in 'photon-jet', E(had) is the energy of the rest hadrons in jet. Ycut is jet resolution parameter (see paper).
The hadronic final states observed with the ALEPH detector at LEP in ${\rm e}^ + {\rm e}^-$ annihilation
XP distribution at c.m. energy 133.0 GeV.
XP distribution at c.m. energy 161.0 GeV.
XP distribution at c.m. energy 172.0 GeV.
The yields of the K*(892)$^{0}$ and $\Phi$(1020) resonances are measured in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV through their hadronic decays using the ALICE detector. The measurements are performed in multiple centrality intervals at mid-rapidity (|$y$|<0.5) in the transverse-momentum ranges 0.3 < $p_{\rm T}$ < 5 GeV/$c$ for the K*(892)$^{0}$ and 0.5 < $p_{\rm T}$ < 5 GeV/$c$ for the $\Phi$(1020). The yields of K*(892)$^{0}$ are suppressed in central Pb-Pb collisions with respect to pp and peripheral Pb-Pb collisions (perhaps due to rescattering of its decay products in the hadronic medium), while the longer lived $\Phi$(1020) meson is not suppressed. These particles are also used as probes to study the mechanisms of particle production. The shape of the $p_{\rm T}$ distribution of the $\Phi$(1020) meson, but not its yield, is reproduced fairly well by hydrodynamic models for central Pb-Pb collisions. In central Pb-Pb collisions at low and intermediate $p_{\rm T}$, the p/$\Phi$(1020) ratio is flat in $p_{\rm T}$, while the p/$\pi$ and $\Phi$(1020)/$\pi$ ratios show a pronounced increase and have similar shapes to each other. These results indicate that the shapes of the $p_{\rm T}$ distributions of these particles in central Pb-Pb collisions are determined predominantly by the particle masses and radial flow. Finally, $\Phi$(1020) production in Pb-Pb collisions is enhanced, with respect to the yield in pp collisions and the yield of charged pions, by an amount similar to the $\Lambda$ and $\Xi$.
Ratio of pT-integrated yields (K*(892)0 + anti-K*(892)0)/(2K-) for different centrality intervals in Pb-Pb collisions at sqrt(sNN)=2.76 TeV. The K- yields are taken from PRC 88, 044910 (2013). In the paper this ratio is plotted as a function of the cube root of the mid-rapidity charged-particle multiplicity density (dNch/deta)^1/3 values taken from PRL 106, 032301 (2011).
The elliptic flow coefficient ($v_{2}$) of identified particles in Pb-Pb collisions at $\sqrt{s_\mathrm{{NN}}} = 2.76$ TeV was measured with the ALICE detector at the LHC. The results were obtained with the Scalar Product method, a two-particle correlation technique, using a pseudo-rapidity gap of $|\Delta\eta| > 0.9$ between the identified hadron under study and the reference particles. The $v_2$ is reported for $\pi^{\pm}$, $\mathrm{K}^{\pm}$, $\mathrm{K}^0_\mathrm{S}$, p+$\overline{\mathrm{p}}$, $\mathrm{\phi}$, $\Lambda$+$\overline{\mathrm{\Lambda}}$, $\Xi^-$+$\overline{\Xi}^+$ and $\Omega^-$+$\overline{\Omega}^+$ in several collision centralities. In the low transverse momentum ($p_{\mathrm{T}}$) region, $p_{\mathrm{T}} < 2 $GeV/$c$, $v_2(p_\mathrm{T})$ exhibits a particle mass dependence consistent with elliptic flow accompanied by the transverse radial expansion of the system with a common velocity field. The experimental data for $\pi^{\pm}$ and $\mathrm{K}$ are described fairly well by hydrodynamical calculations coupled to a hadronic cascade model (VISHNU) for central collisions. However, the same calculations fail to reproduce the $v_2(p_\mathrm{T})$ for p+$\overline{\mathrm{p}}$, $\mathrm{\phi}$, $\Lambda$+$\overline{\mathrm{\Lambda}}$ and $\Xi^-$+$\overline{\Xi}^+$. For transverse momentum values larger than about 3 GeV/$c$, particles tend to group according to their type, i.e. mesons and baryons. However, the experimental data at the LHC exhibit deviations from the number of constituent quark (NCQ) scaling at the level of $\pm$20$\%$ for $p_{\mathrm{T}} > 3 $GeV/$c$.
Average kaons v2 as a function of pT for centrality: 0-5%.
We report the measurement of a new observable of jet quenching in central Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV, based on the semi-inclusive rate of charged jets recoiling from a high transverse momentum (high-$p_{\rm T}$) charged hadron trigger. Jets are measured using collinear-safe jet reconstruction with infrared cutoff for jet constituents of 0.15 GeV/$c$, for jet resolution parameters $R = 0.2$, 0.4 and 0.5. Underlying event background is corrected at the event-ensemble level, without imposing bias on the jet population. Recoil jet spectra are reported in the range $20<p_\mathrm{T,jet}^\mathrm{ch}<100$ GeV/$c$. Reference distributions for pp collisions at $\sqrt{s} = 2.76$ TeV are calculated using Monte Carlo and NLO pQCD methods, which are validated by comparing with measurements in pp collisions at $\sqrt{s} = 7$ TeV. The recoil jet yield in central Pb-Pb collisions is found to be suppressed relative to that in pp collisions. No significant medium-induced broadening of the intra-jet energy profile is observed within 0.5 radians relative to the recoil jet axis. The angular distribution of the recoil jet yield relative to the trigger axis is found to be similar in central Pb-Pb and pp collisions, with no significant medium-induced acoplanarity observed. Large-angle jet deflection, which may provide a direct probe of the nature of the quasi-particles in hot QCD matter, is explored.
Azimuthal correlation between a trigger hadron (TT[8,9]) and recoil jets ($R$ = 0.4, 40 < $p_{T,jet}^{reco,ch}$ < 60 GeV/$c$) in 0-10% most central Pb-Pb collisions at $sqrt{s_{NN}=2.76$ TeV.